Prior to the present invention various methods were available for making methylated phenols such as 3,5-xylenol from isophorone. Methylated phenols such as 3,5-dimethylphenol are important as intermediates for the preparation of antibacterials such as 4-chloro-3,5-dimethylphenol.
For example, B. V. Maatschappij, German Offen. No. 2,529,773 shows the conversion of isophorone to 3,5-dimethylphenol in the gas phase using a Co-MoK catalyst on aluminum oxide, where the catalyst was calcined at 900.degree.-1200.degree. C. There is shown in U.S. Pat. No. 3,803,249 a method of making 3,5-xylenol by acetone condensation. A mixture of acetone, water and tetralin are contacted with a magnesium oxide catalyst at a temperature of 371.degree. C.-510.degree. C. Winkler et al, U.S. Pat. No. 2,369,197 shows the conversion of isophorone to 3,5-xylenol by gas phase pyrolysis over activated alumina at 450.degree.-500.degree. C. Additional procedures for converting isophorone to 3,5-xylenol are shown by F. Wattimena, U.S. Pat. No. 3,641,166 and H. G. Frank, K. Ruhl and J. Turowski, U.S. Pat. No. 4,086,282 involving the employment of methyl iodide to convert isophorone to 3,5-xylenol.
The present invention is based on the discovery that 3,5-dimethylphenol can be made by pyrolysis of isophorone. Catalytic demethanation of isophorone can be achieved with an effective amount of the calcination residue of a mixture of magnesium carbonate and/or magnesium hydroxide and a manganese compound as defined hereinafter.